A cryptic lysis gene near the start of the Qbeta replicase gene in the +1 frame.

The maturation/lysis (A2) protein encoded by the group B single-stranded RNA bacteriophage Qbeta mediates lysis of host Escherichia coli cells. We found a frameshift mutation in the replicase (beta-subunit) gene of Qbeta cDNA causes cell lysis. The mutant has a single base deletion 73 nucleotides (nt) 3' from the start of the replicase gene with consequent translation termination at a stop codon 129-131 nt further 3'. The 43-amino acid C-terminal part of the 67-amino acid product encoded by what in WT (wild-type) is the +1 frame, is rich in basic amino acids This 67-aa protein can mediate cell lysis whose characteristics indicate that the protein may cause lysis by a different mechanism and via a different target, than that caused by the A2 maturation/lysis protein. Synthesis of a counterpart of the newly discovered lysis product in wild-type phage infection would require a hypothetical ribosomal frameshifting event. The lysis gene of group A RNA phages is also short, 75 codons in MS2, and partially overlaps the first part of their equivalently located replicase gene, raising significant evolutionary implications for the present finding.